The "_for-sale" Underscored and Globally Scoped DNS Node Name
draft-davids-forsalereg-18

Network Working Group M. Davids
Internet-Draft SIDN Labs
Intended status: Informational 1 December 2025
Expires: 4 June 2026
 The "_for-sale" Underscored and Globally Scoped DNS Node Name
 draft-davids-forsalereg-18
Abstract
 This document defines an operational convention that uses the
 reserved underscored DNS leaf node name "_for-sale" to indicate that
 the parent domain name is available for purchase. The convention can
 be deployed without disrupting existing operations, and it may be
 applied even when the domain name is still actively in use.
About This Document
 This note is to be removed before publishing as an RFC.
 This document contains a "Note to the RFC Editor" requesting removal
 of Section 7 prior to publication. Please also review the Status of
 This Memo section and other relevant parts before publication,
 particularly Section 8.
Status of This Memo
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 provisions of BCP 78 and BCP 79.
 Internet-Drafts are working documents of the Internet Engineering
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 material or to cite them other than as "work in progress."
 This Internet-Draft will expire on 4 June 2026.
Copyright Notice
 Copyright (c) 2025 IETF Trust and the persons identified as the
 document authors. All rights reserved.
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 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents (https://trustee.ietf.org/
 license-info) in effect on the date of publication of this document.
 Please review these documents carefully, as they describe your rights
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Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
 2.1. General Record Format . . . . . . . . . . . . . . . . . . 4
 2.2. Content Tag Type Definitions . . . . . . . . . . . . . . 6
 2.2.1. fcod . . . . . . . . . . . . . . . . . . . . . . . . 6
 2.2.2. ftxt . . . . . . . . . . . . . . . . . . . . . . . . 7
 2.2.3. furi . . . . . . . . . . . . . . . . . . . . . . . . 8
 2.2.4. fval . . . . . . . . . . . . . . . . . . . . . . . . 8
 2.2.5. Future Tags . . . . . . . . . . . . . . . . . . . . . 9
 2.3. Content Limitations . . . . . . . . . . . . . . . . . . . 9
 2.4. RRset Limitations . . . . . . . . . . . . . . . . . . . . 9
 2.5. Wildcard Limitation . . . . . . . . . . . . . . . . . . . 10
 2.6. Placement of the Leaf Node Name . . . . . . . . . . . . . 10
 3. Operational Considerations . . . . . . . . . . . . . . . . . 11
 3.1. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 11
 3.2. Handling of RDATA . . . . . . . . . . . . . . . . . . . . 12
 3.3. Currency . . . . . . . . . . . . . . . . . . . . . . . . 12
 3.4. TTLs . . . . . . . . . . . . . . . . . . . . . . . . . . 13
 3.5. Ambiguous Constructs . . . . . . . . . . . . . . . . . . 13
 3.6. Robustness . . . . . . . . . . . . . . . . . . . . . . . 13
 3.7. Scope of Application . . . . . . . . . . . . . . . . . . 14
 4. Security Considerations . . . . . . . . . . . . . . . . . . . 14
 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15
 6. Ethical Considerations . . . . . . . . . . . . . . . . . . . 15
 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 15
 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
 9.1. Normative References . . . . . . . . . . . . . . . . . . 16
 9.2. Informative References . . . . . . . . . . . . . . . . . 17
 Appendix A. Additional Examples . . . . . . . . . . . . . . . . 19
 A.1. Example 1: Code Format . . . . . . . . . . . . . . . . . 19
 A.2. Example 2: Free Text Format . . . . . . . . . . . . . . . 19
 A.3. Example 3: URI Format . . . . . . . . . . . . . . . . . . 20
 A.4. Example 4: Asking Price Format . . . . . . . . . . . . . 20
 A.5. Example 5: Combinations . . . . . . . . . . . . . . . . . 20
 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 21
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 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
 Well-established services [RFC3912][RFC9083] exist to determine
 whether a DNS domain name is registered. However, the fact that a
 domain name exists does not necessarily mean it is unavailable; it
 may still be for sale.
 Some registrars and other parties offer brokerage services between
 domain name holders and interested buyers. Such services are of
 limited value when the domain name is not available for purchase, but
 they may be beneficial for domain names that are explicitly marked as
 for sale.
 This specification defines a simple method to ascertain whether a
 domain name, although registered, is available for purchase. It
 enables a domain name holder to add a reserved underscored leaf node
 name [RFC8552] in the zone, indicating that the domain name is for
 sale. The indicator can be turned on and off at will and, moreover,
 it is immediately deployable and does not require significant changes
 in existing services, allowing for a smooth introduction of the
 concept.
 The TXT RR type [RFC1035] created for this purpose must follow the
 formal definition of Section 2. Its content may contain a pointer,
 such as a Uniform Resource Identifier (URI) [RFC3986], an
 Internationalized Resource Identifier (IRI) [RFC3987] or another
 string, allowing interested parties to obtain information or contact
 the domain name holder for further negotiations. Details about
 whether and how such negotiations occur are out of scope.
 With due caution, such information can also be incorporated into
 automated availability services. When checking a domain name for
 availability, the service may indicate whether it is for sale and
 provide a pointer to the seller's information.
 The operational convention described in this document does not
 require any protocol change.
 Furthermore, Section 6 discusses some ethical considerations. In
 particular, the approach in this document aims to promote a more
 equitable domain aftermarket and to minimise the potential for
 unintended commercial entanglements by registries.
 Examples are provided in Appendix A.
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1.1. Terminology
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in BCP
 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.
 Although the document defines an operational convention rather than a
 protocol extension, normative language is used to promote consistent
 and unambiguous behaviours among entities that adopt the convention.
 The term "processor" refers to an entity (person, system, or service)
 that reads, interprets, and takes appropriate actions based on "_for-
 sale" DNS labels, whether manually or automatically.
 The term "for sale" is used in a broad sense and may also refer to
 cases where the domain name is available for lease, or where the
 contractual right to use the domain name is offered to another party.
2. Conventions
2.1. General Record Format
 Each "_for-sale" TXT record MUST begin with a version tag, optionally
 followed by a string containing content that follows a simple
 "tag=value" syntax.
 The formal definition of the record format, using ABNF
 [RFC5234][RFC7405], is as follows:
 forsale-record = forsale-version [forsale-content]
 ; referred to as 'content' or RDATA
 ; in a single character-string
 forsale-version = %s"v=FORSALE1;"
 ; %x76.3D.46.4F.52.53.41.4C.45.31.3B
 ; version tag, case-sensitive, no spaces
 forsale-content = fcod-pair / ftxt-pair / furi-pair / fval-pair
 ; referred to as 'tag-value pairs'
 ; only one tag-value pair per record
 fcod-pair = fcod-tag fcod-value
 ftxt-pair = ftxt-tag ftxt-value
 furi-pair = furi-tag furi-value
 fval-pair = fval-tag fval-value
 ; the tags are referred to as 'content tags'
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 ; the values are referred to as 'content values'
 fcod-tag = %s"fcod="
 ftxt-tag = %s"ftxt="
 furi-tag = %s"furi="
 fval-tag = %s"fval="
 ; all content tags case-sensitive lowercase
 fcod-value = 1*239OCTET
 ftxt-value = 1*239OCTET
 furi-value = URI / IRI
 ; http, https, mailto and tel URI schemes
 ; exactly one URI or IRI
 URI = <as defined in RFC3986, Appendix A>
 IRI = <as defined in RFC3987, Section 2.2>
 fval-value = fval-currency fval-amount
 ; total length: 2 to 239 characters
 fval-currency = 1*%x41-5A
 ; one or more uppercase letters (A-Z)
 ; indicating (crypto)currency
 ; e.g., USD, EUR, BTC, ETH
 ; standard three-letter fiat currencies recommended
 fval-amount = int-part [ %x2E frac-part ]
 ; integer part with optional fractional part
 ; e.g., 0.00010
 int-part = 1*DIGIT
 frac-part = 1*DIGIT
 See Section 2.2 for more detailed format definitions per content tag
 type.
 Each "_for-sale" TXT record MUST NOT contain more than one tag-value
 pair, but multiple TXT records MAY be present in a single RRset.
 Every tag-value pair in the RRset MUST be unique, but multiple
 instances of the same content tag MAY occur within a single RRset
 (e.g., two "fcod=" content tags, each with a different content
 value).
 See Section 2.4 for additional RRset limitations.
 The OPTIONAL forsale-content provides information to interested
 parties as explained in Section 1.
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 If the forsale-content is absent or invalid, but a valid version tag
 is present, processors SHOULD assume that the domain is for sale
 unless a local policy indicates otherwise. For example:
 _for-sale.example.com. IN TXT "v=FORSALE1;"
 _for-sale.example.com. IN TXT "v=FORSALE1;fcod="
 _for-sale.example.com. IN TXT "v=FORSALE1;foo=bar"
 In such cases, processors determine how to proceed. An approach
 might be to signal that the domain is for sale and to rely on
 conventional mechanisms (e.g., WHOIS or Registration Data Access
 Protocol (RDAP)) to retrieve and present contact information.
 TXT records in the same RRset, but without a version tag, MUST NOT be
 interpreted or processed as a valid "_for-sale" indicator. However,
 they may still offer some additional information for humans when
 considered alongside a valid record. For example:
 _for-sale.example.com. IN TXT "I am for sale"
 _for-sale.example.com. IN TXT "v=FORSALE1;fcod=XX-NGYyYjEyZWY"
 If no TXT records at a leaf node contain a valid version tag,
 processors MUST consider the node name invalid and MUST discard it.
 See Section 2.3 for additional content limitations.
2.2. Content Tag Type Definitions
 The following content tags are defined as valid content tags.
 Content tags are optional. Providing a minimum set to allow
 interested parties to engage is RECOMMENDED.
2.2.1. fcod
 This content tag is intended to contain a code that is meaningful
 only to processors that understand its semantics. The content value
 MUST consist of at least one octet.
 The manner in which the "fcod=" content tag is used is determined by
 agreement between cooperating parties.
 For example, a domain name registry may allow registrars to enter a
 "for sale" URL into their back-end system. From that URL, a unique
 code is generated. This code is inserted as the value of the "fcod="
 content tag of the "_for-sale" TXT record of a domain name, as shown
 in the example below.
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 When a user checks the availability of the domain name using a
 registry-provided tool (e.g., a web interface), the domain name
 registry may use the code to redirect the user to the appropriate
 "for sale" URL, which may include a query component containing the
 domain name, for example:
 https://forsale-url.example.com/acme?d=example.org
 The rationale for this approach is that controlling parties retain
 authority over redirection URLs and any other information derived
 from the content tag, thereby preventing users from being sent to
 unintended or malicious destinations or from being presented with
 unintended content. This approach also allows the interpretation of
 "fcod=" content values to be adjusted centrally in back-end systems,
 such as determining which "for sale" URL to redirect to, without
 modifying the "_for-sale" TXT records.
 The following example shows a string encoded using Base64 [RFC4648]
 preceded by the prefix "ACME-" as the value of the content tag:
 _for-sale IN TXT "v=FORSALE1;fcod=ACME-S2lscm95IHdhcyBoZXJl"
 See the Additional Examples section for other possible uses of this
 content tag.
 Note: As an implementation consideration, when multiple parties are
 involved in the domain sale process and use the same mechanism, it
 may be difficult to identify the relevant content in an RRset.
 Adding a recognizable prefix to the content (e.g., "ACME-") is one
 possible approach. However, this is left to the implementor, as it
 is not enforced in this document. In this case, ACME would recognise
 its content tag and interpret it as intended. This example uses
 Base64 encoding to avoid escaping and ensure printable characters,
 though this is OPTIONAL and not required.
2.2.2. ftxt
 This content tag is intended to contain human-readable text that
 conveys additional information to interested parties. For example:
 _for-sale IN TXT "v=FORSALE1;ftxt=Call for info."
 While a single octet is the minimum, it is RECOMMENDED to provide
 more context.
 While a URI in this field is not syntactically prohibited, its
 interpretation as a URI is not guaranteed. Use of URIs in this field
 SHOULD be avoided in favor of the "furi=" content tag.
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 See Section 2.2.4 for a way to explicitly indicate an asking price
 for easier machine parsing.
 See Section 3.2 for considerations regarding the representation of
 non-ASCII data in the content value.
2.2.3. furi
 This content tag is intended to contain a human-readable and machine-
 parsable URI that can be used by interested parties to retrieve
 further information.
 While the syntax allows any URI scheme, only the following schemes
 are RECOMMENDED for use: http and https [RFC9110], mailto
 [RFC6068][RFC6530] (Section 11.1), and tel [RFC3966].
 The content value MUST contain exactly one URI. For example:
 _for-sale IN TXT "v=FORSALE1;furi=https://example.com/foo%20bar"
 URIs MUST conform to the syntax and encoding requirements specified
 in Section 2.1 of [RFC3986], including the percent-encoding of
 characters not allowed unencoded (e.g., spaces must be encoded as %20
 in a URI).
 Section 3.2 provides additional guidelines on character encoding.
 See the Security Considerations section for possible risks.
 Note: References to a URI in this document also encompass IRIs
 [RFC3987].
2.2.4. fval
 This content tag is intended to contain human-readable and machine-
 parsable text that explicitly indicates an asking price in a certain
 currency.
 Price information is commonly published by domain sellers. The
 "fval=" content tag provides a structured format for this purpose,
 enabling reliable machine parsing and reducing ambiguity compared to
 embedding prices in free-form "ftxt=" content tags. For example:
 _for-sale IN TXT "v=FORSALE1;fval=EUR999"
 The information provided in "fval=" is not binding. For current and
 reliable information, interested parties SHOULD engage directly with
 the seller via "furi=" or conventional mechanisms.
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 See Section 3.3 for additional operational guidelines and the
 Security Considerations section for possible risks.
2.2.5. Future Tags
 Future tags may be defined to accommodate operational needs. Future
 content tags MUST NOT alter the semantics of existing content tags.
 A tag name length of 4 characters is RECOMMENDED for consistency with
 the initial tag set and to maintain compact record formats.
2.3. Content Limitations
 The "_for-sale" TXT record [RFC8553] (Section 2.1) MUST contain
 content deemed valid under this specification.
 Any text suggesting that a domain is not for sale is invalid content.
 If a domain name is not or no longer for sale, a "_for-sale"
 indicator SHOULD NOT exist. The presence of a valid "_for-sale" TXT
 record SHOULD therefore be regarded as an indication that the domain
 name is for sale.
 The existence of a "_for-sale" leaf node does not obligate the holder
 to sell the domain name; it may have been published in error, or
 withdrawn later for other reasons.
 This specification does not dictate the exact use of any content
 values in the "_for-sale" TXT record. Parties may use it in their
 tools, perhaps even by defining specific requirements that the
 content value must meet. Content values can also be represented in a
 human-readable format for individuals to interpret. See the
 Additional Examples section for clarification.
 See Section 3 for additional guidelines.
2.4. RRset Limitations
 This document does not impose a limit on the number of TXT records in
 the RRset of "_for-sale" TXT records.
 When multiple "_for-sale" TXT records are present in an RRset, the
 processor MAY select one or more of them.
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 For example, a domain name registry might extract content from an
 RRset that includes a recognizable "fcod=" content tag and use it to
 direct visitors to a sales page as part of its services. An
 individual, on the other hand, might extract a phone number (if
 present) from a "furi=" tag in the same RRset and use it to contact a
 potential seller.
 An example of such a combined record is provided in Appendix A.5.
 The RDATA [RFC9499] of each "_for-sale" TXT record MUST consist of a
 single character-string [RFC1035] with a maximum length of 255
 octets, to avoid the need to concatenate multiple character-strings
 during processing.
 The following example illustrates an invalid "_for-sale" TXT record
 due to the presence of multiple character-strings:
 _for-sale IN TXT "v=FORSALE1;" "ftxt=foo" "bar" "invalid"
2.5. Wildcard Limitation
 Wildcards are only interpreted as leaf names, so "_for-
 sale.*.example." is not a valid wildcard [RFC4592] and is non-
 conformant. Hence, it is not possible to put all domains under a TLD
 for sale with just one "_for-sale" TXT record.
 The example below, however, shows a common use case where a "_for-
 sale" leaf node exists alongside a wildcard:
 * IN A 198.51.100.80
 IN AAAA 2001:db8::80
 _for-sale IN TXT "v=FORSALE1;ftxt=Only 99ドル at ACME"
2.6. Placement of the Leaf Node Name
 The "_for-sale" leaf node name can essentially be placed at any level
 of the DNS except in the .arpa infrastructure TLD.
 Table 1 illustrates this:
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 +================================+================+================+
 | Name | Situation | Verdict |
 +================================+================+================+
 | _for-sale.example. | root zone | For sale |
 +--------------------------------+----------------+----------------+
 | _for-sale.aaa.example. | second level | For sale |
 +--------------------------------+----------------+----------------+
 | _for-sale.acme.bbb.example. | third level | For sale |
 | | with public | |
 | | registry | |
 +--------------------------------+----------------+----------------+
 | _for-sale.www.ccc.example. | third level | See note 1 |
 | | without public | |
 | | registry | |
 +--------------------------------+----------------+----------------+
 | _for-sale.51.198.in-addr.arpa. | infrastructure | See note 2 |
 | | TLD | |
 +--------------------------------+----------------+----------------+
 | xyz._for-sale.example. | Invalid | non-conformant |
 | | placement, not | |
 | | a leaf | |
 +--------------------------------+----------------+----------------+
 Table 1: Placements of TXT record
 Note 1: When the "_for-sale" leaf node is applied to a label under a
 subdomain, there may not be a public domain name registry [RFC9499]
 capable of properly recording the rights associated with that label.
 Nevertheless, this does not constitute a violation of this document.
 One possible approach is for the involved parties to establish a
 mutual agreement to formalize these rights.
 Note 2: If a "_for-sale" leaf node were to appear under the .arpa
 infrastructure top-level domain, it might be interpreted as an offer
 to sell IP address space, E.164 numbers or the like. However, such
 use is explicitly out of scope for this document, and processors MUST
 ignore any such records.
3. Operational Considerations
3.1. DNS Wildcards
 DNS wildcards interact poorly with underscored names [RFC8552]
 (Section 1.4), but they may still be encountered in practice,
 especially with operators who are not implementing this mechanism.
 This is why the version tag is a mandatory element: it allows
 processors to distinguish valid "_for-sale" records from unrelated
 TXT records.
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 Nonetheless, any assumptions about the content of "_for-sale" TXT
 records should be made with caution, particularly in edge cases where
 wildcard expansion - possibly combined with DNS aliases (e.g.,
 CNAMEs) or redirections (e.g., DNAMEs [RFC6672]) - might result in
 misleading listings or unintended references to third-party domains.
3.2. Handling of RDATA
 Since this method relies on DNS TXT records, standard content rules
 apply as defined in [RFC1035] (Section 5.1). This includes the
 possibility of representing non-ASCII data in the content value, by
 using escape sequences (e.g., \DDD or \X notation).
 All text in content values exchanged between systems that are not
 part of a closed ecosystem SHALL be encoded in and interpreted as
 UTF-8 [RFC3629] and conform to the Network Unicode format [RFC5198].
 The allowed subset of Unicode code points SHOULD conform to [RFC9839]
 (Section 4.3), with the exception of %x09, %x0A and %x0D which MUST
 NOT be used.
 See Section 3.6 for additional guidelines and the Security
 Considerations section for possible risks.
 Internationalized Domain Names (IDN) MAY be expressed as A-labels as
 well as U-labels [RFC5890], with U-labels encoded using escape
 sequences as described above.
 Processors MUST be capable of handling such encodings to ensure that
 non-ASCII content values are correctly interpreted and represented.
 Note: When non-ASCII data is used, the ABNF octet limit applies to
 the encoded byte sequence, not the number of visible characters.
 Multi-byte characters will reduce the available character count.
 For example, this TXT record contains two Japanese Kanji characters
 encoded in UTF-8 using octal escapes, resulting in a content value of
 six octets.
 _for-sale IN TXT "v=FORSALE1;ftxt=229円163円178円229円135円186円"
3.3. Currency
 The ABNF in Section 2.1 allows currency codes consisting of one or
 more uppercase letters, providing flexibility to accommodate both
 standard fiat currencies and other widely recognized abbreviations,
 such as cryptocurrencies.
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 The use of standard fiat currencies is RECOMMENDED. When used, they
 MUST be represented by three-letter uppercase currency codes as
 specified in [ISO4217] (e.g., USD, EUR, GBP and JPY).
 The amount component consists of an integer part, optionally followed
 by a fractional part separated by a decimal point (%x2E, ".").
3.4. TTLs
 Long TTLs [RFC1035] (Section 3.2.1) increase the risk of outdated
 data misleading buyers into thinking the domain is still available or
 that advertised prices remain current.
 A TTL of 3600 seconds (1 hour) or less is RECOMMENDED.
3.5. Ambiguous Constructs
 Ambiguous constructs in content values SHOULD be avoided, as
 illustrated by the following example:
 _for-sale IN TXT "v=FORSALE1;fcod=TRIP-confusing;ftxt=dont_do_this"
 The above example is a valid "fcod=" content tag that includes the
 string ";ftxt=" in the content value, which may be confusing, as it
 does not actually represent an "ftxt=" content tag.
3.6. Robustness
 Because the format of the content part is not strictly defined in
 this document, processors MAY apply the robustness principle of being
 liberal in what they accept. This also applies to space characters
 (%x20) immediately following the version tag.
 Alternatively, parties may agree on a more strictly defined
 proprietary format for the content value to reduce ambiguity.
 However, it is out of scope to discuss which mechanisms are put in
 place for such agreements.
 When encountering unexpected, or prohibited control characters in
 "ftxt=" content (e.g., %x09, %x0A, %x0B, %x0D, see Section 3.2),
 processors MAY sanitize them by replacing them with spaces (%x20) to
 ensure correct representation, or replacing them to the Unicode
 REPLACEMENT CHARACTER U+FFFD (%xEF.BF.BD) to signal the presence of
 problematic content.
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3.7. Scope of Application
 The "_for-sale" mechanism relies upon the domain name being
 resolvable in the DNS. This is not guaranteed, for example, during a
 redemption period, in pendingDelete status [STD69], or when the
 domain is DNSSEC-signed but fails validation (i.e., has a bogus
 state).
4. Security Considerations
 One use of the TXT record type defined in this document is to parse
 the content it contains and to automatically publish certain
 information from it on a website or elsewhere. However, there is a
 risk if the domain name holder publishes a malicious URI or one that
 points to improper content. This may result in reputational damage
 to the party parsing the record.
 An even more serious scenario arises when the content of the TXT
 record is not properly validated and sanitised, potentially enabling
 attacks such as XSS or SQL injection, as well as spoofing techniques
 based on Unicode manipulation, including bidirectional text attacks
 and homograph attacks.
 Therefore, it is RECOMMENDED that any parsing and publishing is
 conducted with the utmost care. Possible approaches include
 maintaining a list of validated URIs or applying other validation
 methods after parsing and before publishing.
 Automatically following URIs from "_for-sale" records without user
 consent creates security risks, including exposure to malware,
 phishing pages, and scripted attacks. Implementations SHOULD NOT
 automatically redirect users when encountering "furi=" content tags.
 Instead, processors SHOULD present the target URI to users and
 require explicit confirmation before navigation. This allows users
 to inspect the destination before proceeding.
 There is also a risk that this method will be abused as a marketing
 tool, or to lure individuals into visiting certain sites or making
 contact by other means, without there being any intention to actually
 sell the domain name.
 Domain holders may advertise artificially low prices and processors
 that present "fval=" data to users SHOULD display appropriate
 disclaimers (e.g., "Price indicative only - verify with seller").
 Automated systems SHOULD NOT make purchase commitments based solely
 on advertised prices without human verification.
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5. Privacy Considerations
 The use of the "_for-sale" leaf node name publicly indicates the
 intent to sell a domain name. Domain holders should be aware that
 this information is accessible to anyone querying the DNS and may
 have privacy implications.
 There is a risk of data scraping, such as email addresses and phone
 numbers.
 Publishing contact information may expose domain name holders to
 spam, or unwanted contact.
6. Ethical Considerations
 Although not specifically designed for this purpose, the mechanism
 described in this document may also facilitate domain name
 transactions by professional speculators, often referred to as
 domainers, and those commonly referred to as domain drop catchers.
 Some may view this as controversial.
 However, by enabling domain name holders to more explicitly signal
 their intent to sell, the "_for-sale" approach aims to introduce
 greater clarity and predictability into the domain lifecycle. This
 potentially reduces the advantage currently held by these
 professionals, and fosters a more equitable environment for all.
 Furthermore, this mechanism avoids creating unnecessary dependencies
 on registries for market transactions, which could otherwise
 introduce complexities and potential for unintended commercial
 entanglements.
7. Implementation Status
 The concept described in this document has been in use at the .nl
 ccTLD registry since 2022, when it initially started as a pilot.
 Since then, hundreds of thousands of domain names have been marked
 with the "_for-sale" indicator. See for example:
 https://www.sidn.nl/en/whois?q=example.nl
 The Dutch domain name registry SIDN offers registrars the option to
 register a sales landing page via its registrar dashboard following
 the "fcod=" method. When this option is used, a unique code is
 generated, which can be included in the "_for-sale" record. If such
 a domain name is entered on the domain finder page of SIDN, a "for
 sale" button is displayed accordingly.
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 A simple demonstration of a validator is present at:
 https://forsalereg.sidnlabs.nl/demo
 <NOTE TO RFC EDITOR: Please remove this section before publication as
 per RFC7942.>
8. IANA Considerations
 IANA is requested to add the following entry to the "Underscored and
 Globally Scoped DNS Node Names" registry [RFC8552] :
 +=========+============+=============+
 | RR Type | _NODE NAME | Reference |
 +=========+============+=============+
 | TXT | _for-sale | <this memo> |
 +---------+------------+-------------+
 Table 2: Entry for the
 "Underscored and Globally Scoped
 DNS Node Names" registry
9. References
9.1. Normative References
 [ISO4217] SIX Group, "ISO 4217 Currency Codes",
 <https://www.iso.org/iso-4217-currency-codes.html>.
 [RFC1035] Mockapetris, P., "Domain names - implementation and
 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
 November 1987, <https://www.rfc-editor.org/info/rfc1035>.
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119,
 DOI 10.17487/RFC2119, March 1997,
 <https://www.rfc-editor.org/info/rfc2119>.
 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
 2003, <https://www.rfc-editor.org/info/rfc3629>.
 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
 Resource Identifier (URI): Generic Syntax", STD 66,
 RFC 3986, DOI 10.17487/RFC3986, January 2005,
 <https://www.rfc-editor.org/info/rfc3986>.
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 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
 Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
 January 2005, <https://www.rfc-editor.org/info/rfc3987>.
 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
 Specifications: ABNF", STD 68, RFC 5234,
 DOI 10.17487/RFC5234, January 2008,
 <https://www.rfc-editor.org/info/rfc5234>.
 [RFC5890] Klensin, J., "Internationalized Domain Names for
 Applications (IDNA): Definitions and Document Framework",
 RFC 5890, DOI 10.17487/RFC5890, August 2010,
 <https://www.rfc-editor.org/info/rfc5890>.
 [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
 RFC 7405, DOI 10.17487/RFC7405, December 2014,
 <https://www.rfc-editor.org/info/rfc7405>.
 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
 May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC9839] Bray, T. and P. Hoffman, "Unicode Character Repertoire
 Subsets", RFC 9839, DOI 10.17487/RFC9839, August 2025,
 <https://www.rfc-editor.org/info/rfc9839>.
9.2. Informative References
 [RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
 DOI 10.17487/RFC3912, September 2004,
 <https://www.rfc-editor.org/info/rfc3912>.
 [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
 RFC 3966, DOI 10.17487/RFC3966, December 2004,
 <https://www.rfc-editor.org/info/rfc3966>.
 [RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
 System", RFC 4592, DOI 10.17487/RFC4592, July 2006,
 <https://www.rfc-editor.org/info/rfc4592>.
 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
 <https://www.rfc-editor.org/info/rfc4648>.
 [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
 Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
 <https://www.rfc-editor.org/info/rfc5198>.
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 [RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
 URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010,
 <https://www.rfc-editor.org/info/rfc6068>.
 [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for
 Internationalized Email", RFC 6530, DOI 10.17487/RFC6530,
 February 2012, <https://www.rfc-editor.org/info/rfc6530>.
 [RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the
 DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
 <https://www.rfc-editor.org/info/rfc6672>.
 [RFC8552] Crocker, D., "Scoped Interpretation of DNS Resource
 Records through "Underscored" Naming of Attribute Leaves",
 BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019,
 <https://www.rfc-editor.org/info/rfc8552>.
 [RFC8553] Crocker, D., "DNS Attrleaf Changes: Fixing Specifications
 That Use Underscored Node Names", BCP 222, RFC 8553,
 DOI 10.17487/RFC8553, March 2019,
 <https://www.rfc-editor.org/info/rfc8553>.
 [RFC9083] Hollenbeck, S. and A. Newton, "JSON Responses for the
 Registration Data Access Protocol (RDAP)", STD 95,
 RFC 9083, DOI 10.17487/RFC9083, June 2021,
 <https://www.rfc-editor.org/info/rfc9083>.
 [RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
 Ed., "HTTP Semantics", STD 97, RFC 9110,
 DOI 10.17487/RFC9110, June 2022,
 <https://www.rfc-editor.org/info/rfc9110>.
 [RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
 RFC 9499, DOI 10.17487/RFC9499, March 2024,
 <https://www.rfc-editor.org/info/rfc9499>.
 [STD69] Internet Standard 69,
 <https://www.rfc-editor.org/info/std69>.
 At the time of writing, this STD comprises the following:
 Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
 STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
 <https://www.rfc-editor.org/info/rfc5730>.
 Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
 Domain Name Mapping", STD 69, RFC 5731,
 DOI 10.17487/RFC5731, August 2009,
 <https://www.rfc-editor.org/info/rfc5731>.
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 Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
 Host Mapping", STD 69, RFC 5732, DOI 10.17487/RFC5732,
 August 2009, <https://www.rfc-editor.org/info/rfc5732>.
 Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
 Contact Mapping", STD 69, RFC 5733, DOI 10.17487/RFC5733,
 August 2009, <https://www.rfc-editor.org/info/rfc5733>.
 Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
 Transport over TCP", STD 69, RFC 5734,
 DOI 10.17487/RFC5734, August 2009,
 <https://www.rfc-editor.org/info/rfc5734>.
Appendix A. Additional Examples
A.1. Example 1: Code Format
 A proprietary format, defined and used by agreement between parties -
 for example, a domain name registry and its registrars - without a
 clearly specified meaning for third parties. For example, it may be
 used to automatically redirect visitors to a web page, as described
 in Section 2.2.1:
 _for-sale IN TXT "v=FORSALE1;fcod=XX-aHR0cHM...wbGUuY29t"
 Note: the content value in the above example is truncated for
 readability.
 The use of the "fcod=" content tag is, in principle, unrestricted,
 allowing implementers to define additional uses as needed. For
 example, it may convey arbitrary formatting or conditional display
 instructions, such as adding an extra banner (e.g., "eligibility
 criteria apply") or specifying a style, including color, font,
 emojis, or logos.
A.2. Example 2: Free Text Format
 Free format text, with some additional unstructured information,
 aimed at being human-readable:
 _for-sale IN TXT "v=FORSALE1;ftxt=Eligibility criteria apply."
 The content in the following example could be malicious, but it is
 not in violation of this specification (see the Security
 Considerations):
 _for-sale IN TXT "v=FORSALE1;ftxt=<script>...</script>"
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A.3. Example 3: URI Format
 The holder of "example.com" wishes to signal that the domain is for
 sale and adds this record to the "example.com" zone:
 _for-sale IN TXT "v=FORSALE1;furi=https://example.com/fs?d=eHl6"
 An interested party notices this signal and can visit the URI
 mentioned for further information. The TXT record may also be
 processed by automated tools, but see the Security Considerations
 section for possible risks.
 As an alternative, a mailto: URI could also be used:
 _for-sale IN TXT "v=FORSALE1;furi=mailto:hq@example.com?subject=foo"
 Or a telephone URI:
 _for-sale IN TXT "v=FORSALE1;furi=tel:+1-201-555-0123"
 There can be a use case for these URIs, especially since WHOIS (or
 RDAP) often has privacy restrictions. But see the Privacy
 Considerations section for possible downsides.
A.4. Example 4: Asking Price Format
 Consists of an uppercase currency code (e.g., USD, EUR), followed by
 a numeric amount. See Section 3.3 for additional guidelines.
 In Bitcoins:
 _for-sale IN TXT "v=FORSALE1;fval=BTC0.000010"
 In US dollars:
 _for-sale IN TXT "v=FORSALE1;fval=USD750"
A.5. Example 5: Combinations
 An example of multiple valid TXT records from which a processor can
 choose:
 _for-sale IN TXT "v=FORSALE1;furi=https://fs.example.com/"
 IN TXT "v=FORSALE1;ftxt=This domain name is for sale"
 IN TXT "v=FORSALE1;fval=EUR500"
 IN TXT "v=FORSALE1;fcod=ACME-ZGVhZGJlZWYx"
 IN TXT "v=FORSALE1;fcod=XYZ1-MTExLTIyMi0zMzMtNDQ0"
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Acknowledgements
 The author would like to thank Thijs van den Hout, Caspar Schutijser,
 Melvin Elderman, Ben van Hartingsveldt, Jesse Davids, Juan Stelling,
 John R. Levine, Dave Lawrence, Andrew Sullivan, Paul Hoffman, Eliot
 Lear (ISE), Joe Abley and Mohamed 'Med' Boucadair for their valuable
 feedback.
Author's Address
 Marco Davids
 SIDN Labs
 Meander 501
 6825 MD Arnhem
 Netherlands
 Phone: +31 26 352 5500
 Email: marco.davids@sidn.nl
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